Cleaning & Resurfacing the Head and Pistons on a Kohler 301

Sun Oct 10, 2010 6:38 pm

I'm in the middle of rebuilding the Kohler K-301 in my Cub Cadet 122 so I'll take the opportunity to show you how to clean the top of the piston & block plus resurfacing the cylinder head in your own garage.

My Cub Cadet is a narrow frame with a 12 hp Kohler but the technique is the same.You'll need to remove the tins to get at the head bolts. Break each bolt loose ( I use the tightening pattern ) before removing them. A slight tap on the head may be required to break it free.

It'll probably look something like this

Now rotate the engine so the piston is at the top and both valves are CLOSED. ( It may take an additional rotation to achieve this ) Using a putty knife or razor blade scraper, remove the excess carbon buildup. Keep in mind the block is cast iron and hard to scratch and the piston & head are both aluminum and will scratch or gouge easily. A wire wheel in a drill will work too but be careful not to remove metal, especially on the soft aluminum head. Also be sure to wear safety glasses because the wire will fly out of the wheel.

If your engine has head studs like mine did ( it had a replacement low boss head on it ), you may want to remove the studs. Simply double nut the stud, tighten the nuts against each other and while using the bottom nut, unscrew the stud. ( Use the top nut to seat/bottom the stud ) I highly recommend cleaning the threads with a tap.

Once you have the block cleaned and the head cleaned up( I was able to glass bead the head at work to clean it ), the real fun begins, making sure the head is flat. For this you'll need a new piece of glass( no more than 15 year old, it needs to be flat ) , a piece of wood/plywood , some fine emery paper in 320 and/or 400/600 grit ( full sheets ), a heavy duty stapler ( optional ) and the head off your cadet.

Put the emery paper ( sand paper ) down on the plywood and staple one end down. Slide the glass underneath and staple the other end down. Do NOT put the stapler on the glass as it may break it.

Now take the head, place it on the emery paper and move in a circular motion applying even pressure. Every couple of minutes, lift the head to see how the pattern looks and to blow the dust off the paper. You may use a clean brush if you like. When you have a nice shiny surface, you're done. I spent about 30 minutes of "hand sanding" on the glass plate to finish this head. This picture was taken at the 20 minute mark.

Clean the head with carb cleaner and make sure the spark plug threads are clean too. Clean the top of the block and make sure you didn't get any debris in or on the valve seats. Turn the engine over to make sure.

I use antiseize on the head studs and head bolts. I use the double nut to seat them against the block. ( remember this picture )

Double check your block surface for any debris and place the brand new head gasket on the block.

Place the head and finish putting the remaining bolts in and just snug them down ( I use the tightening pattern )

Now torque the head down in the proper sequence. I use a "three step" method. First time around I tighten them to 1/2 torque value, second time about 2/3 and the final to full torque value.

Now reassemble the engine and I suggest changing the oil too.

You're not done, the final torque to insure longevity will require two more steps. Run the engine for one hour, let it cool and re torque the head to proper torque. ( yes, you may have to disassemble some stuff like the gas tank and gas tank bracket )

Then run it for 4-5 more hours and do your final re-torqueing.

Want to know what may happen if you don't retorque the head? The head will not be seating correctly and you may end up with lean condition. That is what happened to the 122 I got. It ran but smoked like mad.